This invention relates generally to mechanical stokers, and more particularly to a stoker construction which uses inwardly converging tuyere modules disposed about the inner combustion chamber wall to permit easy expansion of a stoker design to accommodate a wide range of different sized combustion chambers with a minimum number of standarized parts. The improved construction may be used in both rotary grate and fixed grate stokers of a wide variety of designs.
Stokers of the prior art have been traditionally designed to custom fit within the wall structure which defines the combustion chamber of a furnace, boiler, or the like. Generally such stokers include a grate for supporting burning fuel, a means for feeding fuel onto the grate and a means for removing ash. Many modern day stokers employ rotating outer grates with stationary central sections which promote better fuel distribution, more even burning, and improved ash removal.
It is also known that combustion can be made more efficient and can be better controlled through the admission of pressurized air, in controlled proportions, to different combustion zones within the combustion chamber. For example, it is now common practice to use air plenums or wind boxes located beneath the fuel supporting grate to force air through the grate upwardly into the burning fuel pile. If desired, separate air plenums may feed separate zones above the grate. For example, in a rotary stoker having a stationary central grate section and an outer rotating ring section, a first air plenum might be used to admit air through tuyeres or air passages in the central stationary section, while a second air plenum might be used to admit air through the outer rotating ring. By separately controlling the air admitted from these two air plenums, combustion can be optimized in accordance with boiler or furnace demands. In addition, the controlled admission of air aids in reducing slag deposits and clinker formation, and also keeps the fuel supporting grate cooler to minimize burn through and promote longer life.
In many applications, it is also beneficial to provide for the controlled admission of air from above the fuel supporting grate as well as from beneath it. The controlled admission of overfire air provides many of the same benefits as air admitted beneath the fire, and also promotes a robust fire through controlled turbulence of the combustible exhaust gases and particulates for a more complete combustion. Prior art stokers which implement the admission of overfire air employ tuyeres which are formed within or formed flush with the inner combustion chamber walls, for directing pressurized air into the combustion chamber from air plenum sources located either within the furnace wall or around the exterior thereof.
A problem with all known prior art stokers is that the fuel supporting grate structures and air admission equipment must, to a great extent, be custom fit to each furnace, boiler or combustion system, since these combustion systems are not usually of standardized sizes. Accordingly, such custom-fit stokers tend to be expensive, considerably more so than if manufactured in standardized sizes. However, inasmuch as there is little, if any, industry wide standardization in the design and construction of boilers, furnaces and other combustion devices, there continues to be a need for a stoker design which will readily and economically accommodate a wide range of different sized combustion chambers with a minimum number of standardized parts.
The present invention provides an economical solution to the aforementioned stoker construction problems by providing a stoker for use within a wall structure which defines a combustion chamber of a given sized inner perimeter. The stoker comprises a fuel supporting grate sized to fit within the inner perimeter of the combustion chamber leaving a predetermined gap between chamber wall and grate. The stoker is also provided with a readily interchangeable outer periphery structure which, when properly selected and attached to the combustion chamber wall, adapts the stoker to conform to the inner perimeter of the chamber. A tuyere defining module is secured about the inner perimeter of the combustion chamber to span the predetermined gap between chamber wall and grate. The tuyere defining module has an outer periphery which conforms to the inner perimeter of the combustion chamber and has an inner periphery which cooperates with the outer peripheral flange structure of the fuel supporting grate to form a baffle.
The tuyere defining module comprises at least one submodule, which can be of a standardized size, and provides a downwardly converging surface for containing fuel. The tuyere defining module has a means receptive of pressurized air, such as a plurality of air passages communicating with an air plenum, for directing pressurized air into the combustion chamber above the grate. The tuyere defining module may, if required, be assembled from a plurality of standardized submodules stacked on top of one another, in stadium fashion, so that the stacked submodules each define part of the downwardly converging surface.
The invention further provides a compartment receptive of pressurized air defined by the outer periphery structure and located directly adjacent the tuyeres for supplying air through the tuyeres into the combustion chamber.
The invention thus provides a means, in the form of stackable tuyere modules defining an outer periphery structure, for adapting a standardized sized stoker to any given sized combustion chamber. By stacking a selected number of tuyere modules, in assembly with one another, the effective size of the fuel containment grate can be adjusted in relatively small, discrete increments to fit the combustion chamber. Finer size adjustment is made possible by providing a selection of different sized standardized tuyere modules.